Apparatus for charged-particle deflection modulation



Nov. 15, 1966 J, GOLDBERG 3,286,123

APPARATUS FOR CHARGBD-PARTICLE DEFLECTION MODULATION Filed June 1, 1962 SIGNAL 3 INPUT F G "o R g 2 OUTFUT I I Z I 2' E 2 l T;

K (I D U E5 6 5| 1 I o 1.5 o +l.5 U SIGNAL DEFLECTION VOLTAGE (UNITS) FIG. 5

INVENTOR JACOB GOLDBERG BY ww ATTORNEYS United States atent Gflice 3,286,123 Patented Nov. 15, 1966 3,286,123 APPARATUS FOR CHARGED-PARTICLE DEFLECTION MGDULATIGN Jacob Goldberg, 4 Garrity Road, Burlington, Mass. Filed June 1, 1962, Ser. No. 199,482 4 Claims. (Cl. 315-17) The present invention relates to methods of and apparatus for charged-particle deflection modulation and, more particularly, to electron-beam deflection-modulation amplification.

In numerous prior-art types of electron-beam amplifiers and similar apparatus, including traveling-wave amplifiers and other velocity-modulation tubes and the like, the generation of space charge has been considered a detrimental and unwanted phenomenon that undesirably affects the stability and other operational characteristics of such apparatus, as by producing an off-axis divergenceeffect upon the beam; and many proposals have been offered and employed to obviate the problems inherent in the presence of space charge in this type of apparatus.

The present invention, on the other hand, is concerned with beneficially employing space-charge effects instead of trying to compensate for or eliminate such effects. In so doing, moreover, the present invention provides a novel method of and apparatus for signal amplification that makes positive use of space-charge beam-divergence characteristics and, startlingly, provides for beam modulation, amplification and oscillation with advantages presently unattainable with conventional traveling-wave and other velocity-modulation devices.

A further object is to provide a novel charged-particle beam modulator that is particularly, though not exclusively, applicable to electron beams.

An additional object is to provide a new and improved amplifier.

Still vanother object is to provide a novel oscillation generator or transmitter employing the beam-deflection modulation principles of the method underlying the invention.

In summary, from one of its broad aspects, the invention relates to a method and apparatus wherein a dense charged-particle beam is projected along a predetermined axis, the beam is deflected off the axis and diverges from space-charge action, and the space-charge diverging beam is then converged to direct the beam further off the axis, thereby to provide amplification of the deflection.

Other and further objects wil be explained hereinafter and will be more particularly delineated in the appended claims.

The invention will now be described in connection with the accompanying drawing, FIG. 1 of which is a longitudinal section diagram of an electron-beam tube constructed in accordance with a preferred embodiment of the invention;

FIG. 2 is a fragmentary section of the output end of a modified tube employing a resonant cavity;

FIG. 3 is a view similar to FIG. 2, illustrating the use of a traveling-wave helix;

FIG. 4 is a similar fragmentary view showing the addition of further deflection means;

FIG. 5 is an experimentally obtained graph illustrating the performance of an embodiment of the invention; and

FIG. 6 is a fragmentary diagram of a modified lens structure.

Referring to FIG. 1, the invention is illustrated as applied to an electron-beam modulation tube 1, though it will be readily apparent that other types of charged-particle beams, such as proton beams and the like, may equally well be generated and acted upon in the manner underlying the invention. The chargedparticle generator or gun is shown comprising heater H for releasing electrons from a planar cathode C, as of the Pierce type, or any other conventional type, a pair of accelerating grids G and G and an apertured electrode A The first grid G is shown biased at a potential V less negative than the cathode potential --V and more negative than the accelerating potential +V applied, to the second grid G The first grid G establishes the total emission or beam current, which is deliberately made'intense or dense to generate substantial space charges; and the second grid G acts with the apertured electrode A which is shown grounded at G, to constitute a first lens for causing the electron beam to converge or project (as at I) into the hereinafter described deflection system D D The deflection system D D may be of any desired well-known type, including magnetic, traveling-wave deflection, cavity or wave-guide deflection or electrostatic deflection types; and is schematically shown in simplified form as a pair of deflection plates D and D substantially equally spaced on opposite sides of the beam axis A-A.

It is to the deflection system D -D that the signal-to-be amplified, or, more generically, the beam modulation effeet, is to be introduced, as by applying the signal input at terminals 3, 5 and along conductor 2 and ground G to the respective deflection plates D and D In accordance with the present invention, as before intimated, advantageous use is made of the diverging or oil"- axis fanning-out effect caused by the mutual repulsion action of intense space chargesthis effect causing the divergence indicated at H just beyond the deflection system D D By employing one or more appropriate lenses L and L of critical lens power and location, the diverging action of the space charge and the off-axis signal deflection of the beam can be interacted with the focusing action of such a lens or lenses so that the beam will be reconverged while the off-axis signal deflection of the beam at D -D may be greatly magnified or amplified. Otherwise stated, a perturbation or deflection of the spacecharge beam off the axis AA, can be magnified by appropriate interacting focusing fields. Since there are no stray or other capacitive effects involved in the signal deflection process, this magnification or amplification is inherently nonresonant and very broad band, extending even from direct current to video frequencies and far beyond, if desired. An extremely high g of the order of from a substantial fraction of a mho up to substantially one mho can be obtained, moreover, as compared with values-of g of the order of thousands of micromhos with presentday gridded tubes and many velocity-modulation devices. High power with efliciencies in excess of fifty percent are also indicated through this gainful employment of the space-charge effect.

In FIG. 1, a pair of lenses L and L before mentioned, is employed to introduce a periodic off-axis deflection modification, each lens comprising a pair of spaced apertures 77 and 7 7 provided with respective intermediate gn'd electrodes G and G To produce the space charge interaction effects necessary to attain the results of the invention, it has been found that each lens must have a focal length f that is related to the substantially constant distance L between successive lenses (or between the final lens and the ultimate target or collector electrode T) by the relationship L/f 4.

Each lens must have its focal length within the distance L separating it from the next lens, and each lens must be positioned in the region, such as II (or III), where the space-charge diverging action is present. Each successive lens projects the beam to the opposite side of the axis AA from that caused by the preceding lens. The axis of each lens is aligned with the orginal beam axis and is thus displaced from the axis of the signal-deflected beam.

Thus, the lens L with its control grid G connected to the positive potential +V interacts with the space charge divergence II of the signal-deflected beam and reconverges the beam and directs it to intersect the axis, thence toward a region displaced upwardly off the axis AA a greater or amplified distance or amplitude shown at P and the next successive similar lens L with its grid 6;, connected to a similar potential +V interacts in the space-charge diverging region III to reconverge the beam and direct it downward across the axis AA an even greater distance or amplitude P and so on, for further successive lenses, not shown, if desired.

A single collector T and a barrier or obstacle T may be employed to respond to changes in beam position to produce single-ended amplified output; or a pair of overlapping collectors TT' may be employed, as shown, to provide push-pull outputs in respective load circuits schematically represented by the blocks R and R The loads R and R are intended to represent loads ranging from output resistors to tuned or tank circuits, such as wave-guide cavities R and R if particular resonance effects are required. Alternately, the modulation-deflected beam could directly feed a resonant wave-guide section or cavity, such as the pair of push-pull cavity resonators R of FIG. 2, the mouths of which are separated by a ground-plate 9' and the outputs of which are coupled out at 9. As another illustration, a travelingwave conductive helix may be employed as at R in FIG. 3. The helix R is shown disposed in a conductive grounded guide or housing B. The use to which the helix R would be put in this device is to respond to the beam directed along its axis by extracting energy therefrom, the helical-path being a slow-wave structure. The advantage of a helix is that it is not resonant and in principle (at least) has very broad band width. Moreover, the process whereby a beam and helix interact so as to induce energy into the helix is also inherently broad banded.

Although this interaction becomes very complex at high frequencies, a sense of what goes on can be had by considering the beam of current as a primary winding threading through the center of a multiturn helix which acts as a secondary connected to a load. If the current in the beam changes with time, the current delivered to the load by the helix will also change, similar to the action with a transformer. The case of a helix and beam is complicated by the fact that the beam threads the helix at a velocity only slightly different from the velocity at which induced signals propagate along the length of the helix, and this magnitude of the difference has many eflects. Nevertheless, the problem is present in both situations of varying the current in the primary in order to induce anything in the secondary; that is, the beam must be density-modulated first. In the case of the present invention, the density modulation is obtained by introducing a knife-edge or equivalent obstacle or barrier into the path of the beam, such as the bottom wall of the conductive housing B, so that more or less of the beam passes the barrier according to the deflection.

Similarly, push-pull-responding output structures of the character shown in FIGS. 2 and 3, corresponding to the push-pull outputs R and R of FIG. 1, may be employed. Appropriate feed-back along an appropriate path or paths F, FIG. 1, moreover, will enable oscillation-generation or amplification feed-back, if desired, as is well-known.

The density of the charged-particle beam, moreover, may be varied to introduce a further modulation that would enable the attaining at the output of the tube 1 of an amplified product of the density and deflection modulation signals. One such type of density modulation is the on-off type schematically illustrated as effectable in the embodiment of FIG. 1 by means of the arrowed block -V which can enable application and removal of the cathode voltage V thereby to signalmodulate the beam-current density.

If desired, moreover, a plurality of deflection means may be employed with the lens structure to increase the off-axis modulation amplitude. Thus, in the system of FIG. 4, a second deflection system D D is disposed beyond the lens L of the tube of FIG. 1. The deflection system D D in an opposite sense to the feeding of deflection signal to the deflection system D D is also energized by conductor 2, though at a later time, controlled by the time-delay network 2', to increase the deflection modulation amplitude.

As an example of a suitable apparatus operating in accordance with the present invention, the distance L may be about 1% inch, as may be the length of the deflection region D D the separation of grid G from grid G and from electrode A and the separation of grids G and G from respective apertured lens electrodes 77 and 7'-7 may be about one tenth of an inch; and the applied voltages may have the following values: V =-200 volts; V :1'48.3 volts; V =+200 volts; +V =+200 volts; +V =+20O volts. Clearly, appropriate magnetic lenses may also be used.

With a tube of such construction, embodying one lens only, namely, the lens L with a value V of 0 volt, V of 16 volts, V of 25 volts, and a lens L with the grid G on the entrance face of the lens, and a voltage V, of 10 volts, in view of this position of G the experimental results of the curves I and I of FIG. 5 were obtained. Along the ordinate of FIG. 5 is plotted the current received at the collectors T, T, and along the abscissa is plotted the signal-deflection voltage applied to the deflection member D The respective curves I and I demonstrate the change in push-pull currents received at T and T, with signal-deflection voltage.

A comparison of the slope of the curves I and I with the curves of P and I' obtained without the inter action with the lens L shows a gain of about 1.25 for this preliminary experimental model.

The deflection and lens systems, moreover, as shown in FIG. 6, may be constructed to produce hollow cylindrical beams, the lens elements 7", G and 7" being illustrated as annular discs or cylindrical devices.

Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A charged-particle beam-current modulator having, in combination, means for generating a high-density charged-particle beam and projecting the same along a predetermined axis, means for signal-deflecting the beam off the axis in a first direction to a predetermined region beyond the deflecting means at which region the space charge associated with the deflected beam has caused the beam to have a predetermined divergence, and beamconverging means at said region, the beam-converging means being adjusted to converge the space-charge diverging deflected beam and to direct the same in another direction intersecting the axis to produce through spacecharge divergence an amplified off-axis deflection, and means for responding to the off-axis beam.

2. Apparatus as claimed in claim 1 and in which means is provided for modulating the density of the chargedparticle beam current in order to obtain at the said responding means an amplified product of the density modulation and the deflection signal.

3. Apparatus as claimed in claim 1, the distance L between the beam-converging means and the responding means having substantially the following relationship with the focal length 1 of the beam-converging means: L/f 4.

4. Apparatus as claimed in claim 1, and in which the amplified elf-axis deflection is at a second predetermined region at which the space charge associated with the UNITED STATES PATENTS 1,659,636 2/1928 Null 330-46 X 2,064,469 12/ 1936 Haefi 328-229 2,179,916 11/1939 Bouwers 315-17 Schlesinger 330-46 X Preisach et a1. 330-46 X Litton 330-46 X Brillouin 315-80 Law et al. 315-17 X Heising 315-3 X Krawinkel 315-17 Overbeek 328-229 Adler 330-46 X Adler 328-229 X Germeshausen et a1. 315-17 JAMES W. LAWRENCE, Primary Examiner.

5 ROBERT SEGAL, DAVID J. GALVIN, Examiners. 

1. A CHARGED-PARTICLES BEAM-CURRENT MODULATOR HAVING, IN COMBINATION, MEANS FOR GENERATING A HIGH-DENSITY CHARGED-PARTICLE BEAM AND PROJECTING THE SAME ALONG A PREDETERMINED AXIS, MEANS FOR SIGNAL-DEFLECTING THE BEAM OFF THE AXIS IN A FIRST DIRECTION TO A PREDETERMINED REGION BEYOND THE DEFLECTING MEANS AT WHICH REGION THE SPACE CHARGE ASSOCIATED WITH THE DEFLECTED BEAM HAS CAUSED THE BEAM TO HAVE A PREDETERMINED DIVERGENCE, AND BEAMCONVERGING MEANS AT SAID REGION, THE BEAM-CONVERGING MEANS BEING ADJUSTED TO CONVERGE THE SPACE-CHARGE DIVERGING DEFLECTED BEAM AND TO DIRECT THE SAME IN ANOTHER DIRECTION INTERSECTING THE AXIS TO PRODUCE THROUGH SPACECHARGE DIVERGENCE AN AMPLIFIED OFF-AXIS DEFLECTION, AND MEANS FOR RESPONDING TO THE OFF-AXIS BEAM. 